The set that contains all possible elements for a particular problem under consideration. Symbol: E. E is defined according to the scope of the problem being studied.

For example, in a problem involving only natural numbers, the universal set is the set of all natural numbers: {1, 2, 3, 4, . . .}. All other subsets involved, such as the even number set {2, 4, 6, . . .}, are taken from this universal set.